How do I stop Blender from adding numbers to end of object names?
This is normal. Blender has been doing this for a very long time and this is what it should be doing. Every object name needs to be unique in Blender so when it encounters an object being named with something that already is a name of another object, it automatically fixes this by adding the numbers and this way making the names unique. If you do not wish to have the numbers there, you can give unique names to all of your objects in the first place.